Converting to Canadian ATPL
As someone who had to convert my Zimbabwe CPL(H), i can say that it was straightforward. Goto Transport Canada website and type in converting licence and read the blurb there. But basicially, you just have to fill in any hours that they require if it was not part of your licence. Then write the exams (fairly simple). Then a brush up for a recommendation ride and finally flight test. As you have a JAA / EASA licence, i doubt there will be any filler hours required. So probably just a couple of familiarisation flights and flight test after doing the exams.
Not sure if you will have to write the SAMRA and SARON exams which are the instrument exams or not. But the transport canada website should give you all that information.
Much easier than going the other way around, that's for sure!
Good luck, Canada is agreat place to live.