I'm an AERE who's been posted to two different Tac Hel units, including one in Pet.
There are two Tac Hel units in Petawawa. Although 427 Sqn is technically under the command of CANSOFCOM, they still follow a lot of regs and rules of 1 Wg. As an example, the SAMA (basically the senior AERE Officer for the Griffon and Chinook) is a LCol at 1 Wg. Thus, despite 427 being special forces, 1 Wg still carries a lot of weight with the unit. The other unit is 450 Sqn, which operates the Chinook. Both units regularly take newbie AVN techs, but I suspect your chances would be better at 450 Sqn due to the role that 427 Sqn provides, i.e. they usually want more experienced folks.
Petawawa is a good place. I liked it and would go back there if given the opportunity.
As for the trg, yes, Tac Hel tends to do more "Army" stuff than other RCAF units. This includes the reg trg already mentioned, field exercises in austere locations, MRPs in the field, HCCR, etc. Plus, (and I know that I'm going to get comments back from this, but it is the truth) Tac Hel units tend to deploy more than other RCAF units (which I loved). This includes both domestic and international ops.