Regarding Canadian taxes, all you need to do is search here on QL and you will find a number of useful discussions and information. Links to a few:

http://www.qatarliving.com/node/84531
http://www.qatarliving.com/node/114350
http://www.qatarliving.com/node/36391

From what I understand you have to cut all ties with the country in order to maintain a non-resident status to avoid paying taxes. It *could* still be your duty to file tax returns each year for all income earned abroad. After having gone through with the immigration & naturalization process just recently, are you sure you want to cut ties.

Organizations like QP are no longer what they used to be 5-10 years ago. They are quite selective these days. You could get lucky and be offered a "Western-Passport-Holder-but-Asian-Origin" package, that may be higher than "Asian-Passport-Holder" package.

With regard to remuneration for a specific job description, there is nothing set in stone (not in QP, not anywhere in this region). The compensation varies wildly and depends on a lot of other factors including passport/nationality etc. At this early stage all you and others can do is speculate the outcome.

My suggestion would be to focus on issues like taxes, perceived and actual savings at both places, work culture, job satisfaction, future plans for your career, etc.