If he really was a Lord he would almost certainly be well documented the Dukes of Bedford family name was/is Russell. He's not, which makes me question the accuracy of the title you give to him.
There was a Caroline Russell, c1743-1811, or to give her her full title, Lady Caroline Russell, daughter of John Russell, 4th Duke of Bedford, who married George Spencer, 4th Duke of Marlborough, in 1762. If she'd had an undocumented son out of wedlock age 15 he wouldn't have been a Lord. John Russell, 4th Duke of Bedford died at Bloomsbury, and I suspect that someone is trying to manufacture an aristocratic background for the John Russell who lived in Canada.
A note on the Ancestry tree to which you refer states that he was "a british ensign under Captain Green. The 31st regiment set out from Glasgow, in April 1776, under Major General Burgoyne to Cork, Ireland and arrived 28 May 1776 in Quebec shortly after the defeat of the Americans."
There were numerous John Russells baptised in England in 1758 - but what's the evidence that he was born in 1758?