Manitoba's premier has seen his approval ratings slide once again, but he remains one of the most popular provincial leaders in the country, a poll suggests.

Brian Pallister saw his approval rating drop to 36 per cent, down five points from 41 per cent last quarter, in the latest quarterly polling data by the Angus Reid Institute. This is down 17 points from his high in the Angus Reid poll in September 2016, when he sat at 53 per cent.

There are likely numerous reasons for the continual slip in ratings, said the report.

"The last three months have seen Standard & Poor downgrade the province's credit rating for the second year in a row, suggesting Manitoba will not be able to prevent deficits over the coming years," it reads.

"The summer also bore witness to continued controversy over the premier's time in Costa Rica, this time centring on the use of his wife's cellphone and email for government business."

Premier Brian Pallister's approval ratings have slid in regular Angus Reid polling since he was elected in 2016. (Angus Reid Institute)

Despite the slide, Pallister is still one of Canada's most popular premiers, tied at third with New Brunswick Premier Brian Gallant. Brand-new B.C. Premier John Horgan sits at 48 per cent, while outgoing Saskatchewan Premier Brad Wall sits on top with 49 per cent.

Ontario Premier Kathleen Wynne brings up the rear with a 17 per cent approval rating, up two points from last quarter.

The poll was conducted from Sept. 5-19 with a randomized sample of 5,466 Canadians. A probability sample of this size with this sample plan would carry a margin of error of +/- 2 percentage points, 19 times out of 20. Manitoba's sample size was 791 with a margin of error of +/- 3.5 percentage points.