The Canada-U.S. Border Covid-19 closure scheduled to be lifted on May 21st, 2020, has been extended another 30 days.
Here is the CBS news link: Canada-U.S. border to remain closed for another month as provinces slowly reopen
And the NPR news link: U.S., Canada Agree To Keep Border Partly Closed For Another 30 Days
For travelers traveling to or from Alaska through Canada for jobs or going home, some sort of proof may be required. There is also a 14-day quarantine, meaning no hotels, restaurants, or any stops other than to get fuel and sleep in your vehicle.
Ammunition note: even though Canadian web sources still claim that travel with 5,000 rounds of ammunition without a special permit is still allowed, varying reports have come to us that some Canadian Customs stations are limiting U.S. travelers to 100 to 200 hundred rounds. The final decision is at the discretion of the border officer. We advise calling the customs station at which you are planning to cross, and check with them on their private limitations as well as any essential travel documentation that they may require.