After checking, no, it really wouldn't (although Parliament seats weren't necessarily divided very fairly before the 19th century reforms, what with rotten boroughs and all that).
Apparently the colonies had around 2.5 million people by that time, with Great Britain at only about 7-8 million. I'd have estimated the former number much lower, and the latter at least twice as high... that does suddenly shed a new light on the American colonists' victory in the Revolution.
True, there was no necessary reason for proportional representation, but I doubt a few MPs for window dressing would have stopped the Revolution. Ultimate power would still have resided in London, and I doubt the colonies would have accepted that for long.
As for the victory of the colonies... I don't think the numbers, one way or another, played a major role. The first revolutionary war in India, which the British won, would have been no contest at all if you just look at numbers. British colonial success often came due to their ability to play native citizens and governments against each other, which also played a major part in the American Revolutionary War.
Hmm... I'd have thought Delhi, Lahore and Calcutta were all larger at the time, but maybe I'm wrong.
