A US drivers license is NOT sufficient for a US citizen to enter Canada, as it does not show citizenship. Whilst US Citizens can enter Canada without a Visa, citizens of most other countries - including people who are present in the US and have a US drivers license - can not, so the Canadian government requires you to be able to prove citizenship before entering.
The only documents that are valid for a US Citizen entering Canada over land are a Passport (book or card), a NEXUS/FAST card, or an Enhanced Drivers License. Enhanced Drivers Licenses are a special form of drivers licenses that are issued by a small number of states (or at least, used to be - I think most have stopped issuing them now) that does state your citizenship on it. It is extremely unlikely that your uncle has such a drivers license.
IF your uncle was able to enter Canada (which he will not be able to!), then he WOULD be able to re-enter the US using his drivers license. Or at least, with no documentation other than his drivers license. As a US Citizen he can not be denied entry to the US, even without proper documentation, such as passport. If he was to present himself at the US border the staff there would use other means to confirm his identity and citizenship, and once they confirmed he was a US citizen he would be allowed enter the US. This will take additional time, and is not a path that should be attempted except as a last resort - but it will work.
So no, your uncle can not travel to Vancouver.