Safe Travels requires a test from specific partners. There are quite a few in the US (CVS, Walgreens, and a bunch of other clinics with multiple sites in various places, like CityHealth here in SF area). The US carriers are also working with providers who will help. United at SFO, for example, has a test partner Color who will do the test, I think they are rapid ones with results in 15 minutes, but you'd need to leave enough connection time to actually do it, wait your turn, get the results, which must come before the departing flight. From what I saw, for Canada, you have to go through AC or Westjet.

Honestly, if I were leaving Canada and departing on a mainland to HI flight, I would see the best option for the carrier you are flying, and make sure there is enough connection time. I know there is a provider at SEA that does it, presumably that works with Alaska, so that could be an option. Might be wise to build in a few hours to connect to go though this. I also know that fully vac'd travelers in US are exempt from HI quarantine without need for pre-flight testing, and while I haven't read the rules for others, I would suspect that if you received an FDA-approved vaccine (ie, in Canada, anything approved that isn't AstraZenica), that might qualify with proof of vac. I'd definitely triple check on that. I'd actually triple check everything to make absolutely sure you meet the Safe Travels requirements,,,,have heard of folks with test results from not approved by HI sites being rejected for exemption, and heading back to CA to get a rapid test to some back. YMMV.

Without judgement, I will throw it out there that at the moment, Oahu just added additional restrictions, and governor is encouraging tourists to not come through the end of October. We are supposed to take our first trip to HI ever in early-mid November, and along with the kids (6 and 3) were very excited, but we are very up in the air right now, and I fear we are going to end up canceling. Would suck, as this was going to be our first real getaway since holidays 2019.