USPHL Premier and NAHL are the only leagues that compare favorably with Canadian Jr A.
We've done this a million times in multiple threads but a good way to think of American Jr Hockey is sort of in this pecking order, and how it SHOULD be split up.
1 - USHL (obvious)
2 - NAHL/USPHL Premier (top of both leagues is very good, bottom of both could be much better)
3 - EHL Premier, NA3HL, USPHL Elite (EHL I think is the strongest overall but these leagues are all pretty close)
4 - USPHL3, EHL Elite, NPHL, MetJHL, WSHL, USPHL Midwest
I think it's pretty safe to say that you can compare the NAHL/Premier to the CJHL, Group 3 to Canadian Jr B, and Group 4 to Jr C.
Since you're asking specifically about the EHL Premier, what I'll say is that it seems that some of the more prestigious teams will get a couple of big names but have trouble putting together depth. The Oilers, Rockets, Monarchs, Cyclones, etc. will always have a couple of standout players, but as a whole their teams don't match up favorably with USPHL Premier teams. To compare to Canadian leagues, I'd put it higher-end Junior B with a handful of players who should be playing up.