to bid time and start a discussion
my "Wrapped In flames general tier list"
using feats from the story only
S tier Dundas thomas Lee Jackson
A tier Grant Hancock johnston most British Corp commanders in Canada east Longstreet
B Rosecrans Pope sherman Sheridan Forrest whoever was in charge of Canada west for the British I admit I forget there name
Unsure everyone else
F tier McClellan
Ironically it was Dundas charged with holding Canada West in 1862, and he did the best of an impossible situation. He's (TTL at least) an A or B rank commander who has very capable subordinates. William Fenwick Williams falls solidly in the B- rank IMO, he can hold a line but would probably be helpless on the attack, while of his subordinates in the persons of Frederick Paulet, Patrick Grant and David Russell are some of the best the British could get their hands on, for divisional or corps command at least.
The corps structure the British army adopts in 1863 would be very much a learning experience, and only Grant would probably have the chops to do it well, and the other commanders would struggle a bit.
On the Union side, Hancock absolutely belongs in the A tier, and he's well on his way to becoming the most recognized general of the war.
did Burnside fumble in this story? I seem to recall him doing a decent job tactically
Well he fumbled a bit, but honestly after Sumners 1863 heart attack Burnside was very unexpectedly thrust into the command slot, expected to go on campaign in Canada, and instead got whacked by the biggest British offensive of the war. So all things considered he did quite well actually.
he also let Lee push him to Washington and lost 2 campaigns to him
Rosecrans and Thomas are then presented as beating Lee back after he's removed
Eh, McClellan's not an F level commander, he did a good job holding the line in 1862 and, to observers at least, maintained the strategic goal of keeping Johnston/Lee out of Washington that year. The scale of the 1863 campaign caught him off guard, but he did mostly succeed in extricating the army to a defensible position (minus Mansfield who got cut off). Whether he could have held the city without relief is a matter of debate for historians, and whether he would have aggressively followed up the campaign compared to Rosecrans - which will be an argument TTL* - is very much up for debate. That at least makes him at worst a D- commander, but I'd place him in the D+ category myself. He doesn't really have the chops to run such a complex operation, and facing a Confederate army which not only outnumbers and can outmaneuver him would be his death warrant I think.
*In case your wondering I think the answers to both questions are a firm no.