The company that is widely used in Canada to train for the Canadian ATPL's is
www.aerocourse.com. You can either sit in their condensed ground schools in Canada, or simply purchase their workbooks and self study. The amount of studying you've done for the UK ATPL's, plus going through all of the questions in the Aerocourse workbooks, might just be enough to get the theory exams done for the Transport Canada exams. These are then locked in for two years, so choose your time wisely because you'll want to avoid rewriting the exams if you can.
The other option is to try and get hired by either Thomas Cook; Thomsonfly; or XL and go deployed to Canada with Skyservice or Sunwing.
Good luck!