I can't help you with Canadian credit cards, but I think you should have at least one frequent flyer account open with Air Canada, and get the CIBC Visa card linked to that. I think you'd be surprised how fast those miles and spend add up.

We have four children and fly quite frequently to Canada and the US. They're all over seven, so not in toddler age, but I think a day flight to the UK is better for you so you don't have to worry about the aggravation of sleeping (or not)!