And, recent history tells us, the US does spy on its allies, its allies' governments and business.
I've always taken the US alarmist position on chinese equipment to at least partially means that they fear not being able to bug the rest of the world as easily once everyone network are not filled with US gears.
IIRC, the US doesn't actually produce any 5G cellular equipment. The alternatives to Chinese equipment are European: Ericsson and Nokia.
EDIT: It appears Intel is working on 5G.
Perhaps not ban, but I would say testing can only tell you so much. It applies to pretty much to any digital system short of exhausting every possible state. Most modern devices can easily have more states than what is possible to test. Moreover most also run software so it's the same as claiming testing is a 100% sure fire way to create bug free software.
Let alone a innocuous back-door. While testing increases the bar for anything malicious to slip by it does not eliminate it entirely. Really it comes down to trust. This applies to all hardware though and I would say everyone is unsophisticated enough to just rely on tests.
Like VHDL was created so the Department of Defense could have something to check ASIC behavior against. I am not saying testing is useless. For instance a malicious actor better be certain that their backdoor can't be found, but they can't be a 100% certain that testing won't find it. It cuts both ways. Testing may not find things, but any adversary may not be sure that their back-door may not be found via testing.
The Five Eyes, often abbreviated as FVEY, is an anglophone intelligence alliance comprising Australia, Canada, New Zealand, the United Kingdom and the United States. These countries are parties to the multilateral UKUSA Agreement, a treaty for joint cooperation in signals intelligence.
The more pertinent question is who the Canadians trust more, China or the US, given the possibility of undetectable backdoors in equipment sold by both. I'd bet on an ally against an adversary.