Get yourself a Canadian multi IR first. It would save a lot of money. Then you can convert. You need to pass all 14 JAA ATPL exams, then conversion courses for the Commercial and and mult IR. You need to pass the JAA CPL flight test then a minimum of 15 hours conversion training for the multi IR. Most of which can be done in a sim. 15 hours is the minimum by the way. You will be put forward for the test when ready not when the 15 hours is complete. So it's important to get the best IR training you can find.
The main stumbling block are those pesky exams.