Question: Don't know if you remember, but I'm your old student Marie Fox from Ontario, Canada. Recently I submitted a manuscript to a US publisher and received a "return" letter saying that I had a good story, but there were too many grammar and spelling mistakes. If you do remember me, you know I am a stickler for grammar....
Answer: Of course I remember you, Marie. You had that great wilderness story going. Good to hear from you. This may come as a surprise to you, and to many others, but when the US formulated a rebellion in 1776, they also started to use their own grammar and spelling rules.
Even those change over time. If you read a classic, say LITTLE WOMEN, you will find that many words used to be hyphenated that no longer require them, now. To-day and To-morrow were once t he rule! Now they'd be a Big Mistake.
One thing you can do to help is to run the US version of spell check, when you plan to submit to a US publisher.
And yes, in the US that's spell check -- not cheque. If you lived in the US, I'd be your neighbor, not neighbour, and red would be my favorite color, not colour...and so on.
The Brits, including Canada, have their own grammar and usage rules, as well. For instance the use of apostrophe s, to show possessives. In Britian, an ordinary name, like Sam, gets an apostrophe S to show possession. Sam's. But if a name ends in S the apostrophe gets no following S, the apostrophe alone is enough to show possession in the Queen's country.
Thomas' car, belongs to Thomas in Canada.
Thomas's car, belongs to Thomas in the US.
But in the US a name ending is S DOES get both the apostrophe and S to show possession, unless the S shows a plural possessive. Then it gets the apostrophe alone... Go figure.
To make things even more complicated, many US colleges teach grammar and usage from the Strunk & White style guidebook, but they were British and their rules of grammar are British.
And finally, if Thomas were a whole family and the car belonged to all of them, it would be:
The Thomas' car -- even in the US.
Anyway, my point is that things are different down here in the Southern provinces. So you might want to give your finished ms. a run with US spelling and grammar check, before sending it along to a US publisher.