I would have trouble trusting the time estimate, at least my online applied work permit was not issued and I applied February 29th.
I would believe actually that in general if you have the right documentation for a CUSMA/USMCA (previously NAFTA) visa at the border. The treaty text says in Chapter 16 section C part 1, "Each Party shall grant temporary entry and provide confirming documentation..." These treaties have been ratified and I don't think there has been evidence of an ICT visa being denied at a port of entry since this would effectively be a treaty violation unless it was denied due to a normal reason not related to covid. For this reason these visas are still available also to canadian citizens entering the US for similar reasons. However I think Canada can still deny you a flight to Canada so you will be unable to each a border to apply.
They granted me an ICT permit at the land port of entry last week, but maybe it is highly situational. I am a US citizen though and so am covered by the treaty, if you need to provide biometrics then I guess you are probably not.