I don't know about all the various pre-paid plans. Have you considered changing to the one "regular" (postpaid) plan TM has? It would give you unlimited text and data in Canada (data at Edge speeds) and voice to Canada and U.S. (and 100 other countries when in Canada) for 20¢/min.
IF you are frequently in Canada, might be worth considering. Cost is $50 for first line, $30 for 2nd, $10 for lines 3,4, and 5.
IF roaming is available on your prepaid plan - the prices you quoted seem correct from the web site. Make re you turn "data when roaming" off so you don't eat up your prepaid balance by all the stuff that runs in the background.