The crucial distinction is which half is in which “half-in” agreement.
They are not offering Canada conditions that the UK would have wanted.
This potential deal for Canada comes with compromises which would obviously be unacceptable to the UK (e.g. no full voting rights).
Does anyone actually know publicly what is and isn't the deal for associate membership?
At least here (in Canada) I'm not seeing any concrete details.
No, nothing public, we are all speculating. But we can surely guess at 99% that Canada would get no voting power, being that we are in North America and Canada isn't interested in that kind of arrangement.
Likely as unacceptable to Canadians.
EEA nations (Norway, Iceland etc) have found them acceptable, and preferable to fully joining up.