I've emailed over thirty five potential supervisors and did not receive any positive response. Should I keep emailing? I've sorted out a list of professors from few Canadian Universities and I've sent customized emails after reading their papers and detailing in short on why I am particularly interested in their research and how it relates with my goals. This took a lot of time for just one email. Most have replied by saying they don't have suitable projects in their labs or are not accepting Masters students. I am bit worried now that I am nearly towards the end of my list of potential supervisors. Should I find more professors and broaden my research area of interest, as suggested by some senior friends? I am an international student and don't have any publications although I do have research experience. Could my lack of publication be a factor for all the rejections? My average GPA is  3.6/4.3 and my field is Biology.
Professors are quite limited with funds and resources (or already have a full team). The likelihood that someone who emails out of the blue to be a suitable choice is slim. Some places probably need a commitee to hire, as a safeguard against discrimination and errors.

You are far better off looking for universities with open positions, I think, or strengthen the connections with professors who already know you (and might write a recommendation letter for you). 

Also, publications are way better than grades, research experience is very valuable (at least in maths, I suspect other fields are similar).