You previously entered on just your passport. Until the ETA came in, you didn’t need anything to enter Canada as a Brit. The passport itself was sufficient to permit entry. You’d know if you’d been issued a Temporary resident permit (it’s A4 size and is folded up and stapled into your passport), you’d only have been issued one if they deemed you inadmissible to Canada but allowed you entry anyway (due to it being for the public good) or if you wanted to stay for longer than the permitted 6 month period.