how do you fine people see magi celebrating the holiday's?

anyone celebrating the Holy Days (the source of modern "holidays") of the Christian year would follow the religious and social practices of the time - there's not really much of a summary in ArM terms yet, but Reams Of Power: The Divine has a bit.
It also briefly covers Islam & Judaism.

There may be something in the forthcoming City & Guild supplement.

(Abe probably means "do they celebrate Christmas with Santa Claus and presents?", to which the answer is a resounding NO!)

As for the other half of the question - do magi celebrate the Christian Holy Days? Most magi ought to be at least notionally Christian - the Divine is known to be real (so Atheism is a Delusion Flaw - not a rational tenet holdable by anyone...) - they are part of the Christian world (unless they live in eg Islamic lands).
They might be Jewish.
They are unlikely to start out Pagan - paganism is essentially extinct in Europe in ME times.

They might well convert to worshiping pagan beings as a result of personal encounters (eg powerful Fae) - but they are almost as likely to have a personal encounter with an Angel (good!) or Demon (bad!).
The arrogance of most magi, and belief in their own power, limits their regard for other supernatural entities...

acturally no I didn't mean that at all.