Hello Juan P.
I have traveled to Canada twice without a return flight, the first time my immigration officer was super nice, He asked me who you come to visit? I say :My husband... and he stamped my passport and let me in, I left 6 months after(Just the time you are allowed with visa)..... The second time , same question, same answer, but this time the immigration officer didn't like it so much, so he passed me to a second immigration office who was very tuff asking many questions about me and my husband, if I was working in Canada, How did we manage the payments if i was not working, if my husband was at the airport waiting for me , if I was sure he was outside, etc...For me was very useful that I have a copy of my husband approval letter as sponsor, my husband invitation letter to visit Canada, with the address of his house (the same for the application file), his telephone, his signature and a copy of his passport, I told her that she can call him if she wanted and I explained to her the way we manage our payment Is with my savings and a bit of income from Mexico, that my intentions were not to work in Canada, only to visit my husband in the meantime the sponsorship approval get process.... My advice to you will be: don't get nervous, bring with you the letter, and prove of your relation, maybe a picture etc, tell them you only come for a visit and that you are not going to stay longer in the country because you have things to do in Mexico, In my opinion is better if you go out of Canada and don't ask for a visa extension but that's a personal decision. Good luck, everything will be fine!!!!