You need a valid passport to both apply and to travel. Would wait and see what happens regarding the interview. Nothing is set in stone yet. Have you been together for a long time? Imagine you haven't lived together a 1 year. Is she willing to get married and sponsor you? The process will likely take12 months or maybe more. Do you have a lot of proof of your relationship and have you spent a lot of time together? Are you both employed and will she be able to financially support you when you arrive in Canada? Will she need supprt from family members and are there family members that would support you if necessary. Given your lack of status in the UK you need a strong application and relationship proof.