like, maybe the extended use of the time portal caused a slight tear in space and time somewhere else in the city, and occasionally a small portal opens and people of other Earths (fandoms) come out... and also a result, somehow a part of their world appears

like if a character from flash arrives, the star labs building is suddenly present someplace in vancouver, or sam and dean bring the bunker, but there's also now suddenly supernatural monsters cropping up around the planet

oh.. and tho it's set in the continuum series, you don't have to stay in vancouver, you can go anywhere on the planet if you like

of course non-natives would be watched by alec/carlos/julian closely, to make sure the finale's utopia future still happens

and if someone wanted to play kiera, you could just say that old alec made her a tech thing, so she can travel back and forth from now or 2077 as she wished (hmm that can be a plot too, for certain characters to visit the future)