Chippawa is on the Welland Canal now? Not the Welland River?
Here is the obvious difference between 1862 and 1814, which I don't think you've grasped the nettle of - in 1862 means exists for Royal Navy warships to cross from Lake Ontario to Lake Erie. In 1814 the RN squadron on Lake Erie had been destroyed by Perry's squadron and there was no way of reconstituting it. In 1862 when the canal opens a horde of gunboats will close down the Niagara river, the Welland River and be on Lake Erie. Hence the time factor.
The US have two weeks from their own port of Buffalo becoming open to navigation (mid-April) to the RN ascending onto Lake Erie. In that time the US has to win enough to have stopped the RN coming into play. This is pretty difficult.
Oh, and hope the Canadians don't pull out some of the 39 heavy mortars they have and bombard Buffalo harbor whilst the ships are still icebound. The US has say three months of relative helplessness to such an attack before they can get their ships out (same to Detroit).
Yep, ice is no fun
However I will let Canadian Canucks very helpful map demonstrate the terrain and geography
Difficult? Of course, which is why I said it matters who has what there at the time action begins.
Don't assume difficult means easy victory for either side
By the way, what is to keep American gunboats built during the winter on Lake Ontario from causing trouble? Rochester and Sacketts Harbor are on that lake, are ports, have rail and Erie Canal connections to the rest of the state and and is a natural place to build gunboasts
Indeed Sacketts Harbor is where warships were built during the last war
To seize the Lakes you must do it one at a time if driving west... securing Ontario, Erie, then the choke points for each, then you still have to get past Detroit to threaten the other 3 lakes
Certainly not an easy task