Cheapest place to buy cash in Canada?

A travel habit I picked up from my father I guess... his problem solving solution was to carry a lot of cash... and the Canadian border guards always ask me if I have "enough cash"... not sure if it's a serious question, or they're being insulting, one guard made me reveal all my cash hiding spots to him so he could count the bills... what a pain in the ass, maybe he was fishing for a donation.

I suppose if it's a serious problem, Ben Franklin can solve it on his own without help from Robert Borden.

Thanks for the input everyone!