I am also an outland (British) applicant and did my medical and biometrics in UK before coming to Canada on my latest trip. For me personally it was more convenient that way as I wanted to "clear up" pre-existing historical medical issues with a British panel physician rather than someone in French-speaking Quebec. It's up to you how you do it really. Also getting biometrics and medicals done before I came meant I had less things to "do" once I was here.
As regards ETA's, these are issued in visa-exempt countries (such as UK) so you don't need temporary resident visas if you are entering Canada via air. Just have a return ticket and make sure the trip is no longer than 6 months. You can always apply to extend it when you're in Canada if necessary, or apply for an Open Work Permit.