Main bit of advice if going common law is to document VERY carefully and thoroughly that you are cohabitating - with official supporting documents, like lease, insurance, utilities, whatever - that shows when you began living together. The common law living together one year minimum is a strict legal requirement - one day off or not clear evidence at the time of applying when it began means you were not common law at time of applying and NOT eligible. The onus is on you to demonstrate it.
This is particularly important when the period of cohabitation is just barely over a year (understandably if a couple has been living together eg five years it's less of an issue when it began.) Things like living in shared housing with others can make that more challenging.
And yes, for purposes of applying, marriage does make it somewhat easier (the 'legal' aspect of being a spouse is clear, mainly need to show the relationship is genuine).