Do I need to get l2 extension at border?

Hi, I'm Canadian and my husband's l1 extension has just recently been approved. For my l2 extension do I have to go to the US/Cdn border or is there another way to get approval?

You can either go to a POE or file I-539. Usually cheaper to go to a POE (and certainly a lot faster) because it's $6 at a POE and $320 using I-539.

Thanks Steven. Does it have to be a Canadian/US POE or can I go to the Mexican/US POE?

Any Class A POE, which means any US international airport, CBP pre-clearance in Canada or elsewhere or virtually all land border crossings.

L-2 is so simple I wouldn't have thought it was a problem at any POE frankly. All they need is proof you still qualify (i.e. marriage certificate and a copy of your husband's I-94 or I-797) and your Canadian passport.