MG Chemicals makes good stuff, so I wouldn't worry about the brand. Others would be Kester, Mutlicore (Henkel), Indium, AIM (American Iron & Metals), and Alpha Metals for example, with various choices of flux type, and % of flux content. Kester and AIM are easier to find in my experience, and from the right place, can be had less expensively than Indium, Multicore, or AlphaMetals. All-Spec is usually good on Kester, and Stanley Supply is also running a sale on Kester right now.
Kester 44 would be one to look at IMHO (offer both
60/40 and
63/37 alloy, rosin core, flux core = 66, which is 6.6%; links are for .025" diameter). Not sure of a specific vendor located in CAN though, and I don't know how bad shipping across the border will impact your wallet.
As mentioned, the differences between metric and imperial measurements regarding diameter aren't really a concern (close enough will do). Dave's accustomed to metric units (what most of the world uses), so that's what he stated in the video. So if say .025" is the closest to what you're after for solder diameter, then go for it. That happens to be a very nice size IMHO, as it's usable for both PTH and SMD while still allowing for a good bit of control as to how much is fed to a joint.
You can always fold it over on itself and twist if you need more solder for say tinning something like a 10AWG wire if needed (reduces the time needed). Can't go smaller though, so if you find you need it, then you'll have to buy some. But the folding trick can keep you from having to buy so many different wire sizes (fewer larger sizes needed).