Going with the WI...
He'd make an attempt at implementing some of his populist, "anti-politician" agenda, like cutting MPs' pensions and expenses. But, as in OTL, he'd be faced with recalcitrance from his own caucus(some of whom apparently hadn't calculated the financial impact of renouncing the pension, prior to getting elected), and back down.
The difference in the ATL is that Manning would actually be the PM, so he'd be the subject of way more media scruitny, and end up with even more egg on his face when he reverses course on his populism. He'd try to cut a few meaningless perks here and there as compensation, but the damage would have already been done.
On social issues, he'd probably try to bring in some sort of law to restrict abortion(such legislation was not completely ruled out by the Morgentaler decision), and end up provoking a lot of backlash from all ends of the political spectrum, especially after a few of his backbenchers got up and made some intemperate speeches about it. Best takeway for the "pro-lifers": A largely symbolic bill passed by parliament saying something like "We respect the rights of the provinces to legislate abortion as they see fit."
re: the third person of Manning's holy populist trinity, immigration: Anyone who has spent time eavesdropping on the conversations in a Canadian donut shop can tell you that there actually would be a lot of support for a reduction in immigration. However, even if he ever had been seriously contemplating that(and I can't recall the exact wording of the Reform platform), once he got into power, he'd realize that it's not as simple as just signing an order to kick 'em all out. There are whole host of considerations, not least of them economic, to take into account. He'd likely just end up doing what subsequent Liberal and Conservative governments did, ie. tilt the process more toward "business class" immigrants, and tighten up the refugee screening process. But he'd be more overtly popuist about doing it, try to sell it to his base as a tough-minded, harda$$ed crackdown on those queue-jumping, welfare-pillfering, turban-wearing foreigners.