Hi Ricardo,
Road trips are fun... you can drive in snow, right?
I haven't been over the crossing in a while, but all reports are that it is tight. If you have all your paperwork, you and the gf should be fine. The problem is sometimes there is a long wait (summer weekend traffic is the worst). There are other crossings, see map. Sumas on highway 9 is my favorite, but the I-5 route is impressive. If you take that route, please be sure to get off in Bellingham and take the alternative route along Chuckanut Drive. You will not be sorry.
Sumas
There's also the route from Vancouver Island and taking the Victoria ferry, entering at Port Angeles. In any case you'll have to go through customs and they
will quite likely stop every car to ask for ID, but as long as you're not a drug runner or terrorist, you should be fine.
This map of webcams shows the current lines at the border (just click on the little cameras):
http://www.wsdot.wa.gov/traffic/
Have a great trip! If you decide to come through Seattle, tell us and we'll round up some NW hospitality for you.