Almost certainly made by Johnson Controls as are like 90% of all the batteries in North America.
I'd guess that battery to be an H6 which will work, maybe, except in the very cold. An H8 gets you 800cca, Autozone's website says for an extra $18. My local Car Quest beat Autozone by $50 for an H7.
I've got an MkIII Jetta and an H8 (the old Group 49) battery will just barely fit, its 900cca. I don't know if that'll fit your MkIV but if it does I'd get it considering you live in the frozen north you can use all the power you can get. In lead acid batteries nothing trumps size and weight for capacity and in the real cold nothing beats capacity for getting your car started. This is not a place to skimp, you don't want to be in the dead of night when you absolutely have to get somewhere and have the car not start.
Along with CCA, a VERY important factor is reserve capacity (since Ah ratings seem to be nearly impossible to get). I'd go for 150 rc at a minimum.
Think of it this way: CCA tells you how much oomph is available in the cold. Ah or RC will tell you how long it will be available. If your battery is marginal, then the CCA will fade quickly - during the glow plug warm up - leaving you without sufficient amps to start the engine.
A 94R battery case will fit in the '03 Jetta, and it probably will get you more battery capacity as well. So what if it lops a little outside the official footprint - like the above posters have said, the more battery the better.
If you have a Sam's nearby (yuk - I hate recommending that company for anything, but it is the best battery and deal I found) check out the 49 (H8) batteries under the Duracell name (made by EastPenn, a very good battery company). H8 fits nicely in the Golf/Jetta chassis and you can select enough amps to fulfill your needs.