Hi & welcome to the forum.
Dont know what kind of job or level you'd be at compared to what you are doing here, but generally outside of London a £54k salary + a £4k car allowance in the
UK would be considered to be half decent.
£1600 left for expenses after rental housing & council tax - I'd say you'd be good even with a couple of small children.
On the basis you know what the other expenses will be out of the £1600 - were you thinking that you'd need to also put £XXX away each month
You'd be working with folks that likely earn a lot less & manage OK - then others that would earn more than you & have a lot less housing & other expenses
Maybe its me, but £1250/mth for
accommodation may be a bit on the high side. If you take the position [if it were me] I'd relook at other quality rentals that could save you a couple hundred pounds a month
The UK [living there] is different than Canada, your standad of living is what you make it - generally expats living in the UK almost always whinge & try to compare 'its not like back home- we did this that and the other different' - try not to do this.
In Canada we tend to worry way too much about money [the government & media do that to us], in
Europe they have a social blanket. If your move is about trying to stash away money from your disposable income - then yes, you may or may not be able to do that - only you can budget those things.
IMO, as long as you muck in & knuckle down, enjoy the experience, take it for what it is - you & your family should be fine.
Try to imagine what its like for a new immigrant to Canada coming from the UK, Australia, SA or NZ - the worries of adjustment along with 'shall my standard of living be OK'.
As long as you dont get home sick - just make the move to the UK as though you are taking a job or making a move across the other side of Canada from where you live now. Hey its only a 6 -7 hour
flight back across the atlantic (point to point)
Enjoy the experience, the kids will fit it easy - its a chance opportunity that may not come your way again, or you may have multiple moves to different countries in your working career ... I'd had four moves during the 70's & 80's - to Bermuda, OZ, NZ & the US [minimum of 2 years in one place then back to Canada first for a while then onto another country] & yes we had children with us at those times.
Hope this helps
Disclaimer: I am not an immigration expert & anything that I post on visa & immigration is based soley on more than 30 years of personal experience & interaction with the UKBA & Home office.