Complex sentence: Cartoons did not have a regular forum in Canada, however, until John Henry Walker's short-lived weekly "Punch in Canada", the Canadian version of Britain's humorous "Punch", debuted in Montréal in 1849, featuring cartoons by Walker.
Split into simpler sentences: Cartoons did not have a regular forum in Canada, however, until John Henry Walker's short-lived weekly "Punch in Canada" debuted in Montréal in 1849. The magazine was the Canadian version of Britain's humorous "Punch", and featured cartoons by Walker.