Unfortunately no one here can guess or guarantee what will happen at the border since this decision is entirely up to the immigration officer you encounter. As a UK citizen, you should be OK. However there's no guarantee. As a UK resident you should be granted a visit of six months by default. However the immigration officer can also allow you in for only a shorter period of time (i.e. not the full six months) or deny you entry completely.
My recommendations would be as follows:
1) Don't lie. If you are asked a question, answer it truthfully.
2) Don't provide too much information. Only answer the questions you have been asked and keep it brief unless asked for more details.
3) Behave like a visitor. You are only allowed to visit until you become a PR. This means you should behave like a visitor at the border. Don't pack like you're moving here and don't talk like you're moving here (i.e. don't say you're coming to live in Canada). Show proof that you are only coming for a visit and evenaully plan to leave (i.e. have a return flight, bring any documentation that shows ties to the UK such as rental agreements, property ownerships, bank accounts, employment or schooling proof, etc.).
4) Pay all of your PR application feels now ($1040) even though you are not ready to submit your application. Have the receipt with you as proof that your husband plans to sponsor you to come to Canada once you are married.