As usual, Antrium, an excellent idea.
Adam Island is a good bet for those looking for twins, since all his cities have "Adam" in them but are modelled on an another city/jurisdiction or class of cities/jurisdictions, e.g., Adamyoto ~ Kyoto or similar Japanese, Adamsburgh ~ Edinburg or similar Scottish, Adamiian Island ~ Hawaii, Rio de Adam ~ Rio de Janeiro, Brazil.
For people without fertile minds like me who have thinly fictionalised the major and capital cities in my RL country of Canada, it's easy, but I'll add some vague details to help the twinning process. I'm sure Domnonia and I could announce some easy twins -- evil twins separated at birth, most likely!

So in approximate order of RP'd population:
Schweindorf = Toronto: Any large city insecure about being a "world class" city is a good match; animal slaughtering history also helpful; cosmopolitan helps; tolerant; smug; biggest city in country also a good match. [My current home.]
Mont Royaume = French Montreal : Any large city obsessed with having a better culture than economy in its home nation is a good match; religious history, esp. RC, very helpful; francophone or language purity; freewheeling, funloving and slightly corrupt also good; high levels of organised labour and business red tape. [Occasionally nice place to visit, wouldn't want to live there.]
Georgetown = Vancouver: Granola-eater heaven; cosomopolitan; liberal; Southern California-style; aging hippies and dopesmokers; close to nature (esp. ocean and mountains), conservation conscious; port city. [Nice place to visit, one ex-wife and others live there now, home of (Paul) Hyde and the Payolas.]
Zalevfyerma = Calgary: social, economic and religious conservatism; Slavic heritage; economy boom-and-bust, esp. energy; devil-take-the-hindmost social service net. [Never been, not keen to go.]
Nordentor = Edmonton: Relative-liberality in an illiberal province/state; provincial capital. [Brief business trip in November, cold but otherwise fine; looks like most other cities of its size and is friendly as these cities go.]
Ville de Hochelaga = Quebec City: RC, French and francophone heritage; government and tourism dominated local economy; collectivist politics; good architecture and history. [Visited it but it was extremely unfriendly to foreigners (i.e., English Canadians like me, with a good working knowledge of French, a keen interest in local history, and the willingness to buy anything flag or playing card related). I will never return.]
Kolashek and Saint-Visage-Osseux = Winnipeg and St. Boniface: Cosmopolitan; Slavic, French, English and misc. bg; labour friendly but politically diverse; RCism and Orthodoxy big; furtrading history; transport hub and manufacturer. [Passed through twice on X-Cda roadtrip, never got a chance to look around; home of the Guess Who.]
Kingsmount = English Montreal: Impudent linguistic minority (as only anglophones can be!); "Westmount Rhodesians," as described by Rene Levesque and Bowser & Blue; very economically productive; obsessed with equality and language rights. [One ex-wife came from here.]
Worthington = Hamilton: rustbelt; steel industry; university town; more greenfields than brownfields as one might not suspect; overshadowed by Schweindorf=Toronto; overshadows Magnificent Falls/Beau Sault = Niagara Falls; Escarpment and associated creeks. [Out and proud Hamilton nationalist by birth.]
Sax River/Valley = southwestren Ontario: Sax-Caughburgh = Windsor (Saxe-Coburg-Gotha being the former name of the Royal House of Windsor), auto manufacturing; Middle Sax = London (seat of Middlesex County), quasi-rural, smug, tri-national British heritage including Black Donnelleys bloodfeud, some auto mfg. in nearby towns; Upper Sax = Kitchener-Waterloo-Cambridge-Guelph, university towns, German heritage. [Bicycle-camped through most of the closer places, never been to Windsor or London in a meaningful way.]
Drewburgh = Halifax: Scottish origins but small cosomopolitan city; big harbour and port; major naval base; big university town; heavy on high and low arts; lots of museums and cultural institutions; big fish in a small pond; inviting, friendly and welcoming; a little chip on shoulder from faded glories, but hardly noticable except foreigners like me identified as "Upper Canadians." [Visited repeatedly in the offseason, would relocate there if I didn't care about being close to family.]
Chapeauxdix = Victoria: provincial capital, major naval base, and English Ville de Hochelaga or Northern Drewburgh. Quaint and smug, longer history than usual. [Never been.]
Potato Island/Princetown = Prince Edward Island/Charlottetown: Small island subsiding on spuds and tourists. RP'd it into becoming a single political unit and joining mainland Braunekuste = New Brunswick. [Never been, considered excessively touristy, but nice and flat for cycling.]