Incredibly simple really.
There are 2 ATPL exams, SAMRA & SARON plus an I/R exam to be done.
After that just an I/R flight test and the issuing of the licence. I converted a NZ CPL into a Canadian ATPL in 2001 and it cost no more than $2000 and took about 5 days. All the pre-study was done prior to arriving in Canada and the exams were on demand.
One word of caution though. Some Transport Canada employees have different takes on the rules/regs of converting. I did mine through a central Canada office and it was easy. The guy who I tried to deal with in the BC office did a lot of hemming and hawing and told me it was impossible.
Good luck