Room is about 12 x 16 x 8 ... Budget less than 1500 (WITH SHIPPING TO CANADA) ... Been looking at Rythmik 15hp and SB-13 ultra and Pb 12 plus. ... Any other suggestions?
As mentioned, SonicBoomAudio (SBA) is SVS' authorized Canadian distributor. At $1,599, the SB13-Plus is already over your price cap before you add shipping and taxes (s&t). The PB12-Plus is $1,399 + s&t, which would put it over your price cap as well.
Given the size of your room (1,536 cu.ft.), a PB12-NSD ($749 + s&t) would work very well, as would dual PB-1000s ($499/ea. + s&t). And if you go duals, I believe SBA still offers a 5% discount on the second sub.
I don't see any mention of two subwoofers and if you don't already have, I don't see mention of a room analyzing program.
If you want to get the best out of one or two subs (don't matter) you'll need room analyzing capability.
If you simply want a recommendation of a decent ID subwoofer, then pretty much, anything in that price range by SVS, PSA or Rythmik will fill the bill nicely. They're all making good stuff and nobody has complaint one about either of these ID manufactures of subwoofers.
My additional recommendation, buy the sub and buy a room analyzer program so you can get the best out of the subwoofer you choose to buy. Just saying.
An aside, if shipping and taxes are a consideration, you have some way cool stuff in Canada in the form of "Funk Audio." It might be outside your budget but in a sense of the word, it's domestic and there may be a price advantage to be had.