I agree with Zyox in most part. For me the road was not so complicated as largely depends on where in JAA you do your training. Initialy i wanted to do it in the UK,but i have change my mind since every school i went to wanted me to do appx.15-20 hrs of flying including ME wich can be quite costly.
Instead i took alternative route and did it in my home country where it took me only 5hrs to convert my licence into JAA one. It is very dependant on what school you chose to use as you know that they are money hungry biatches and they'll sell you anything they could.
After all you are already a fully licenced ICAO pilot,so i really don't see what's all the fuzz about converting it...but that's the way it goes.
Same goes for ATPL exams,they are not easy (14 books each 500-700 pages on average) and you have to finish those in 18 months from the starting date of the first passed exam,if not you will have to do all of them again.
Any multi crew job will also require you to have a MCC done woth 20 hrs in full motion jet and some ground school as well.
If you are close to your 1500hrs mark you are better off to wait and get your ATPL in Canada,because then the things change radically. You only have to do two exams instead of 14 and your licence becomes automaticaly JAA ATPL.
If you need further info on what schools to pick i can give you some leads,so you can PM me if you wish and i'll try to help you as much as i can with advice.
Skydrol