Question: How long did the bombing of a Toronto–Montreal–London–Delhi route of Air India have an effect on Canada-India relations for?

Context paragraphs:
Canada–India relations: Canada–India relations, or Indo-Canadian relations, are the longstanding bilateral relations between Canada and the Republic of India, which are built upon a "mutual commitment to democracy", "pluralism", and "people-to-people links", according to the government of Canada.  In 2009, bilateral trade between India and Canada was at about C$4.14 billion.  Most notably, the bombing of Air India Flight 182 by Canadian residents, killing a vast quantity of Canadian citizens, had effects on relations for about 20 years.  India's Smiling Buddha nuclear test added strains to the relationship between the two nations, with allegations that India broke the terms of the Colombo Plan.  Although Jean Chrétien and Roméo LeBlanc both visited India in the late 1990s, relations were again halted, albeit temporarily, after the Pokhran-II tests.  India and Canada are taking steps to become strategic partners, with Prime Minister Stephen Harper making a state visit in 2012.  Both are former British colonies and full members of the Commonwealth of Nations, with Canada being home to one of the largest Indian diasporas in the world.

Air India Limited: Air India Limited is a company that was formed as National Aviation Company of India Limited by the government of India to oversee the merger of Air India and Indian.  The company was renamed as Air India Limited on 26 October 2010.  It was incorporated under the Companies Act 1956 on 30 March 2007 and was owned by the Government of India based at the Air India Building in Nariman Point, Mumbai.  The Company was created to facilitate the merger of the two main state-owned airlines in India: Air India, with its subsidiary Air India Express and Indian, together with its subsidiary Alliance Air (was called Air India Regional for about 6 years from 2011 to March 2017).

Air India Building: The Air India Building is a 23-storey commercial tower on Marine Drive in Nariman Point, Mumbai, India.  The building served as the corporate headquarters for the Indian national airline, Air India, up to 2013.  There are at least 10800 sqft of space on each floor of the building.  In February 2013, Air India officially vacated the building as part of its asset-monetisation plan, and shifted its corporate office to New Delhi.  The Indian Airlines House was chosen as the airline's new headquarters.  However, the airline still retains the 21st, 22nd and 23rd floors in the building.

Air India destinations: Air India flies to the following destinations as of January 2017.  This list does not contain destinations served by subsidiaries Air India Express or Alliance Air.  For all the destinations ever served by Air India, see the Air India timeline from 1932 to 2011

Air India One: Air India One (also referred to as AI-1 or AIC001) is the call sign of any aircraft with the Prime Minister or President of India on board.  Air India is the national airline of India.  The aircraft is operated as VIP flight by the Indian Air Force (IAF).  The IAF's Air Headquarters Communication Squadron, based at Indira Gandhi International Airport (formerly Palam Air Force Base) in New Delhi, is in charge of operating these aircraft.

Vasu Chanchlani: Vasu Chanchlani (born July 1, 1952 – September 7, 2014) was an Indo-Canadian serial entrepreneur, philanthropist and trans-nations builder.  He is co-founder of the Sigma Group of Companies and a founding member of the Canada India Foundation.  He is also an investor in dozens of companies globally consisting of start-ups and turn-arounds.  He is best known for his efforts towards improving Canada-India relations through his philanthropic activities and engagement with Indian Diaspora to serve bilateral interests of both Canada and India.

Haj subsidy: The Haj subsidy is a subsidy given to Indian Muslim Hajj pilgrims by the Government of India in form of discounted Air fares on Indian Government owned Air India.  The program has its origins in British colonial era.  In post-colonial era, the Government of India expanded the program in 1959 with the Hajj Act.  The subsidy initially applied to Indian Muslim pilgrims traveling for religious reasons to Saudi Arabia, Syria, Iraq, Iran and Jordan.  Haj subsidy started in 1954, as an idea initiated by the then government, with flights between Mumbai and Jeddah.  Additional flight legs were added over the years, and since 1984, all Haj traffic has been shared by Air India and Saudia, the national carriers of India and Saudi Arabia.The monopoly of these airlines has proven the most contentious point of the subsidy with some Muslims objecting to it by claiming that the real beneficiary is Air India as the subsidy is actually a discount on an overpriced air fare.  There have also been requests by Muslims to withdraw subsidy including some Muslim Parliament members as it is against Islam even it was beneficial.

Air India: Air India is the flag carrier airline of India.  It is owned by Air India Limited, a government-owned enterprise, and operates a fleet of Airbus and Boeing aircraft serving 90 domestic and international destinations.  The airline has its hub at Indira Gandhi International Airport, New Delhi, alongside several focus cities across India.  Air India is the largest international carrier out of India with an 18.6% market share.  Over 60 international destinations are served by Air India across four continents.  Additionally, the carrier is the third largest domestic airline in India in terms of passengers carried (after IndiGo and Jet Airways) with a market share of 13.5% as of July 2017.  The airline became the 27th member of Star Alliance on 11 July 2014.

Canada India Foundation: The Canada India Foundation is a Canadian non-profit organisation established in 2007.  The main stated objective of CIF comprises promoting Canada-India relations through their active intervention in public policy which would cover domestic policies and bi-lateral issues affecting the Indo-Canadian community, including issues such as culture, education, trade and investment, immigration, diplomatic, political, and strategic relations.

Air India Flight 182: Air India Flight 182 was an Air India flight operating on the Toronto–Montreal–London–Delhi route.  On 23 June 1985, the Boeing 747-237B serving the flight (c/n 21473/330, registration VT-EFO , "Emperor Kanishka") was destroyed by a bomb at an altitude of 31000 ft .  It crashed into the Atlantic Ocean while in Irish airspace.  It was the first bombing of a 747 jumbo jet.  A total of 329 people were killed, including 268 Canadian citizens, 27 British citizens and 24 Indian citizens.  The incident was the largest mass murder in Canadian history, and the deadliest incident in the history of Air India.  It was the deadliest terrorist attack involving an airplane until the September 11, 2001, attacks.  The bombing of Air India 182 occurred at the same time as the Narita Airport bombing.  Investigators believe that the two plots were linked, and that those responsible were aiming for a double bombing.  However, the bomb at Narita exploded before it could be loaded onto the plane.

Supporting paragraphs: Canada–India relations Air India Flight 182
Answer: about 20 years