Yeah, I grew up with both Colman’s (the powder in the yellow can) and French’s always in the house. French’s was used for sandwiches. Colman’s was used for cooking.
A full British breakfast demands hot English mustard for the bangers, bacon, and puddings (black and white).
Colman’s, BTW, is available as both powder and paste.
I like roast beef sandwiches with mild to medium creamy (mayo-based) horseradish sauce. Straight horseradish is a bit too powerful for me.
I’ve always likened it to what’s sold here as “Chinese mustard”. The flavor is largely the same. I love hot food, not just capsicum, so I will happily slather either of them on a ham sandwich.
I like English mustard. But in practice I use Maille more often. Both are easy to find in Canada, even in small towns.
I’ve only been to the Carnegie Deli once, and I ordered the tongue sandwich. I chose unwisely.
A relevant video: The Most BIZARRE and FORGOTTEN Sandwiches of America
I’ve just made SPAM® salad. I used the box grater instead of the meat grinder. Easier to do, and easier to clean. We don’t keep Miracle Whip around, so I had to buy some when I went grocery shopping. A small jar was on sale for $6.99, The large jar (typical mayo jar size) was $7.49. So I guess we’ll have MW around for a while.
My mother used to make what she called “chopped olive” sandwiches. Basically, chopped up black olives and either mayo or Miracle Whip. I really liked them as a kid.
We had them with cream cheese. Not often, because it’s seriously high fat.
Decided to take the plunge. I bought a jar of Marshmallow Fluff and I made sure that I have creamy peanut butter.
Currently don’t have any white bread in the house, but the next time I do, I’ll finally try a Fluffernutter. Or maybe just a half.
The rest of the jar? I’m making Whoopie (pies).
Ditto. My impression was that it was a common luncheon item when I was a kid, but I haven’t seen it since.
Keen’s, no matter what the label says, is an English mustard. You can get it either prepared and ready to use, or as a mustard powder, which you prepare yourself. But that’s as easy as adding water to the consistency you want. And it is hot; it is a staple in my home, for baked ham, and ham sandwiches, and the like. But be careful; a little goes a long, long way.
Colman’s is about the same. I’ve seen it in southern Ontario supermarkets a few times. Keen’s is much more widely available, and just as good.
As for horseradish, I know that you’re in southern Ontario, and for years, “Susan’s” was the hottest you could get there. And it was fiery. Pretty much limited to southern Ontario, and only available through butcher shops and specialty food stores, unless you went to a fancy restaurant, where it would be served with your prime rib of beef. I have no idea if Susan’s is still available, but you might try, well, specialty food stores and butcher shops.
(Hint: A half-teaspoon of Susan’s would really add some zip to a Bloody Caesar. 
)
Oh, do please report back with what you think!
Chopped olive sandwiches? My first grade crush, Eileen, used to eat the same sandwich every day. Her mother would spread Miracle Whip on bread and then slice black olives to put on it. (She sliced them across, not lengthwise, so they looked like Cheerios from Hell.) The same sandwich every, single day. I was once offered half of one. I was…uh, unimpressed.
I dislike all olives to this day and place the blame solely on Eileen’s mother.
I’m glad you specified a Whoopie is a kind of pie. Without the parenthetical, I would have thought you were into something kinky. 
For especially sticky forms of kink. IMO most folks prefer slippery over sticky for that.
Although I must say that even as a tween when I first heard the term “fluffernutter” it sounded vaguely sexual / “dirty” to me.
Still haven’t eaten one 50+ years later. Sounds disgusting.
Has the mercury warnings in tuna made tuna fish sandwiches less popular?
My family rarely ate fish. I guess our mercury levels are ok.
don’t forget Whoopie cushions/pads