Hi Wilma,
I am not sure what Westjet's qualifications are right now, but I would say that your qualifications should be of interest to them. They are a low-cost carrier in Canada operating a fleet of Boeing 737NG's, however, your qualifications would almost certainly be of interest to Air Canada also, despite the fact that they do not operate Boeing 737's at present.
No Canadian company will be prepared to talk to you unless you have a Canadian ATP. Your JAA or any other licence is a permanent qualification-- no foreign authority can "take it away" from you. Many pilots hold licences in various countries, such as Canada, the US, possibly JAA, and others. The onus is only on you to keep your JAA licence valid, if you desired to do so.
If you do get your Canadian ATP, there is an easy administrative procedure to add your foreign Boeing 737 type rating if you have flown the 737 within the last year. Total cost-- about 5 minutes of your time and $30 Canadian dollars.