I am just going to speak from my own experience but please remember all experiences are different since the determination is always at the discretion of the IO.
When I flew to Canada, I did not have a return ticket but I did have my bf with me. They did not ask me for proof of my return but still wanted to know when I expected to be traveling back. Then they were interested in how I would support myself. I told them that my bf's family was letting me stay with them and that they would be taking care of me. While I was in the office, apparently they had went outside to talk to his parents and make sure that information was indeed correct so make sure you have a story to back you up. Generally though as long as you proof you have no intent to overstay, that you are aware of the visitor terms, that you will obey those terms, and you have some financial support with money to return home then should be fine.
Once again remember every IO and experience is different. If you aren't flying with a return ticket then I would advice that you bring proof of your ties back home. This could include but not limited to: bank statements, bills, house lease, rental agreement, letter from employer expecting your return, appointment letter from a doctor, etc. Don't show all this to them unless asked. They may ask and they may not. But best to be prepared for the worst anyway even if it does turn out for the best.
