Strong economic growth, improving household finances and aging vehicles will be behind the sales boost in the US.
Global growth was a moderate 1% in August.
Scotiabank says Canadian auto sector will only add 0.2 percentage points to overall growth, compared to 0.7 in the US.
The bank has revised its 2013 forecast for Canada to 1.735 million from 1.72 million units.
Sales will continue to be driven by pickup trucks and crossover vehicles.
Vehicle sales up 8% in July and August over 2011, led by double-digit gains in South America.
Japan and Russia lead worldwide growth.