According to Bud-- :

At connections rated 100A and less (like circuit breakers) you can only
use wire at its 60° ampacity rating.

At connections rated over 100A (or marked for wire larger than #1) you
can only use the wire at its 75° ampacity, maximum. For 125A that is
minimum size #1 with 75° insulation (like THWN). I agree with John that
you also need to consider the hot roof.

[Do you have that connection/ampacity rule in Canada Chris?]

I don't recall seeing a rule just like that, but I don't have occasion
to look at sort of thing very much, and my CEC book is quite old now...

I _suspect_ our code doesn't shift temperature ratings based
purely on the ampacity. More based on _use_ (feed vs. circuit,
motor vs. resistive etc), conditions (eg: length, conduit,
burial, conduit fill etc) and cable type of course.

My vague comment re #4 was for 100A indoors, not in conduit etc.
I missed the significance of the routing, and I should have been
clearer it was for 100A not 125A... Oops.

My 100A garage feed is underground - 110'. Direct-burial-rated
Al #3 triplex. Would have been #4 if copper. The cable was
chosen by the electrician thru discussion with the inspector
when I balked at the price of #4 copper.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.