chai,
ta khun thai... Requirements for a TRV are here: http://geo.international.gc.ca/asia/bangkok/site/visitor-en.aspx
The applicant MUST prove to immigration they will return because of strong ties to their country. Such evidence as bank account (with lots of money in it), ownership of land/business, children of applicant... anything that would show immigration that you have to come back after the visit to Canada.
Your boyfriend's letter will probably make the decision easy for immigration to deny the application. I recommend you and your boyfriend read/research www.cic.gc.ca and this forum and others like this one before you apply.
Good luck.
canthai
