I'm in the American Midwest (North and South Dakotas and Minnesota). In the summer, it gets above 100 degrees F and humid and gross. We totally skip Fall and go straight into winter, dropping from the High 70's to readily below freezing within the span of a month. Spring is odd, as it starts to get above freezing, and everybody starts running around in shorts and T-Shirts (Even though it is still below 50, which is reasonably cold by "normal" standards). There are a few decent sized cities, but most of it is rural farmland, woods, and lake areas.
I imagine the area would be ripe with Deer and Migratory Bird pokemon, loads of the "varmit" pokemon (Ratata, Linoone, Eevee, etc), as well as other variety of Fox, Wolf, and other small animals. Water types would be common among the Lake areas, but fresh water types rather than ocean/sea types (Mostly small/medium fish, turtles, etc.). Winters would see just about every variety of Ice pokemon. Summer would see a whole array of bugs. Cave dwellers would be scarce if any, though rock and ground types that don't exclusivly live in caves would be around, but in smaller numbers than mountinous regions. Zubats would come out at night for sure during the warmer months. The farmlands would have plenty of Boffalant, Miltanks, and Tauros Also, I picture some Castforms being around, as controlling the local weather would be more than beneficial for farmers. Large, strong Pokemon (Like Rydon, Machamp, Drilbur, Diglet, Mamoswine, etc) also being common farm Pokemon, for obvious reasons.. I imagine Growlithe/Arcanine (As well as other fire types) being a VERY common pet for snow removal and keeping warm in the STUPIDLY COLD WINTERS (We get to -40's around late december and January, plus it gets windy too) and because they seem like good pets, and for hunting purposes... (Assuming Hunting is still a thing...). Really, we'd have lots of Rapidashes, everywhere. Them being Fire types and Horses and all.
Personally, I'd want an Arcanine and a Braviary. Mostly for getting around really. Braviary would be great for just flying about in the warmer months, and Arcanine for when it's colder or if I'm in a hurry. I'd also have a Zangoose and a Hariyama for helping out with things like Shoveling Snow, Heavy Lifting, and because they seem like good battlers. Professionally? I'd want to be a Pokemon Ranger. Flying around, being a Dearring Doer of Dearring Do. Maybe, also train people to ride pokemon... That's a skill I'd want.
Things that don't exist in Pokemon, but I could see around these parts: Some variety of Grass/Ice pokemon that ISN'T abamasno, but more of a pasture-ish pokemon. I'd have to say the "Legendary" pokemon of the region would be the illustrious Jackalope Pokemon and a Native American-esque Thunder Bird (But not Zapdos. Ours would have a Sound based Electric Move as its signature moe.). There ought to be (at least in the forest/farmland areas of America) a Fire/Grass type, due to the common brush fires and controlled burns in those areas. Another thing we might have in the midwest is a Fire/Ice type. Though it seems counter intuitive, Snow can polarize light and intensify Sunlight, also, consider the dual nature of the mid west to go from crazy hot in July to stupid cold in January. Finally, a Fighting/Ice Pokemon who would be fast, have crazy legs, and be quite the runner. It would be wolf/coyote flavored looks, and be common among those "Black Belt" types in the area (We'll give it a hidden ability that makes all of its Ice Moves get Priority to make it useful. 6 weaknesses and 3 resistances isn't good, and I want it to be cool). And since every region needs that ONE pokemon that just makes you shake your head and wonder, "Why?" The midwest would have a normal rock type that would look like a field plow, and evolve into a tractor. Yup.
I had an idea for a bigger city like New York or London or somewhere that was a sewer rat that was a Poison/Normal type...