replacing line to the garage (canada)
You might as well use that conduit for all it's worth

A 3/4", schedule 80 PVC conduit is capable of holding 3 6AWG stranded THWN wires and a 10AWG stranded bare copper ground, good for 60A.  Considering that your 12/3 cable is likely to be a harder pull down that conduit, both because it's a cable (vs individual wires) and because UF at that size is made using solid wire, vs the stranded wire you get in THWN that size, I would use the individual wires here instead of wrestling an alligator of a cable down a conduit for no good reason whatsoever.

GO BIG OR GO HOME

There is absolutely no reason to use a panel as tiny as the one you suggest in this application.  For not much more money than what your itty-bitty panel cost, you can get a 24-space, 100A, main breaker panel and an accessory ground bar kit for it, which will be large enough to be reused in your new garage for that matter. The main breaker being 100A isn't an issue here, since its simply a cheap way to get a local shutoff switch for all power to the garage.

In the main panel, you can then use a 60A breaker for the feeder, which means you have enough power to handle most things you'd want to do with even an expanded garage, and certainly plenty of power for your tools as of now.  As to branch circuits, I would have one 20A circuit for lights and the minifridge, a 20A multi-wire branch circuit (using a 2-pole, 20A breaker) for the power tools (assuming you're only running one tool at a time), and a spare 20A circuit provisioned (for a window air conditioner or the likes).  This leaves plenty of headroom for a dust collector, and/or a second 20A, 2-pole circuit for more power tools for that matter.

TORQUE ALL LUGS TO SPEC

Note that you should torque all loadcenter and breaker lugs to their manufacturer specification with an inch-pound torque wrench or torque screwdriver.  In the US, this is now required by 110.14(D) in the 2017 NEC, and is a good idea anyway to keep your electrical system from losing you the race the way Greg Biffle's infamous lugnuts did.