Going to Canada, use the VFF to keep your SG till past 2023.
Good thing about VFF is that the earning cycle is cyclic, ie, not a fixed 12 month period of earning status.
Going to Europe, put in your KF # so that you earn points in that one, the points can then be used to redeem for VFF if you decide you want to, or for KF Vrooms, or for J flights around Asia.
Just make sure that you do make use of these points before they expire, as they have a fixed 4 year life span.
If flying Y, then maybe collecting VFF miles/points is ok, but if flying SQ J, better to put in your KF #, as you collect miles and also elite miles, which help you attain or retain tier, they (SQ) might be more helpful if you have tier miles with them.
These are what I would do, of course, I am not saying you have to do the same, you could put in your VFF # into all the bookings, but as VFF is not in a large alliance, its a hard thing.
If you want to, you could also put in your KF # into all the bookings, both the Canadian trip, and the Europe trip, but no tier miles for premY on SQ's partners, only on their own flights, (SQ's own service and metal).
In the end, you could too, put in your VFF # into both bookings.
Don't book any flights with FB (Flybuys) Aust, as you can't pick your fav seats, either in the FB booking system, or in the operating airline's system.
OffT, I made one booking on the FB website for a partner flight, (Air)NZ, paid via FB, and now I can't pick my fav window seat, and wait times to the (Air)NZ phones are a wait time 2 hours.
OnT.