He was a big supporter of the Erie canal, so if he became Governor, he might lay some ground-work to speed that along? The obvious POD is to get him to reject the offer of military command, which was devised specifically to get him out of the political race. If he stays in politics, he may well well. This means someone else gets to be in command in his OTl position-- quite probably someone who has more 'formal' experience than 'mere' militia command. This issue led to trouble for Rensselaer in OTL (officers didn't want to take orders from a 'jumped-up militiaman'), which played a big role in the failure of his campaign in the Battle of Queenston Heights. So another commander, leading an ATL campaign, may well do better. I could see the USA winning a Queenston Heights equivalent. (On the otherhand, the ATL circumstances may well prevent Brock's death.)