I regret not posting it before Canvas 2025, but hopefully it'll be useful for people playing it in 2026. All letters are 5 pixels tall, and most 3 pixels wide (some 4, a few 5). I've also included a few Cyrillic letters and the digits.
I tried to make it even smaller, but it gets really funky.
I hate how Щ looks
If you don't mind having a few six pixels tall letters:
Ш (for reference), Щ, Ц (same problem as Щ), and У (it's weird to use Y in its place, but I kind of forgot to add it).
Of course, this will depend on space, plus personal style. I'm not claiming this is the only way to do things, it's just a viable "font" for people struggling with text in the canvas to use as starting point.
(I actually use a similar strategy with diacritics in the Latin alphabet. Specially ⟨Ç⟩.)
I didn't notice Ц in the original post, I thought it's Ч
I didn't include Ч because it's easy to sub it with 4, Volapuk style.