Difference between Bank and Insurance: Background
Both Banks and Insurance companies sell Life Insurance. According to the existing regulation banks are not allowed to sell insurance products other than Travel or Creditor Insurance in their branches. The most banks though have an independent insurance company (e.g. BMO Insurance, RBC Insurance, TD Insurance etc) which can sell you insurance and some of them offer Life Insurance.
The difference between Life Insurance offered by banks and insurance company is quite simple. Whereas banks offer typically more simple products such as e.g. Term Life Insurance, many insurance companies are able to provide more complex products such as Universal or Whole Life insurance. You need to consider following when you are buying directly from a bank or an insurance company: in this case you are offered products from one provider only but there are ways to compare life insurance products across multiple providers.
Insurance Tip Related to buying Life Insurance
Insurance broker can often get better insurance rates: A good and experienced life insurance broker can navigate you through many question marks, compare for you premiums across dozens of different companies and often get lower rate than you would get on your own (e.g. because brokers may have some air to offer discounts on insurance products due to the large insurance volumes they make).