TN Visa for Canadian and Mexican Professionals in the States

The TN status is a specific status granted to Canadian and Mexican professionals working in the U.S under the NAFTA agreement.

All you need to apply for this status is a signed offer letter from a U.S based company, and a specific job title (One of the designated "professional jobs" by the NAFTA trade agreement between Canada and the U.S). Here is more information:

https://travel.state.gov/content/visas/en/employment/nafta.html

There are certain professions/job functions that they accept: 

http://www.nafsa.org/_/file/_/amresource/8cfr2146.htm

You can apply for a 1 year TN or a 3 year TN, depending on your company. The TN visa is not formally considered a work sponsorship visa, because you don't need any legal assistance (beyond the offer letter). However, some companies consider it a "sponsorship," so it's always good to double check. 

OPT visa: When to apply.

Hello!

The OPT visa is a working visa intended to give college graduates working experience. For most people, the visa gives a year of "practical training." However, if you have a STEM major, then you can apply for an extension, which gives you 17 months in the U.S.

You do not have to have a job offer when you apply for the OPT! You can apply via unemployed, however, once your OPT is in effect, you have 90 days to find a job. Notice, date of the visa going into effect and the date you receive your OPT card does not necessarily match.

Don't be like me; apply for your OPT ahead of time! I lost time (I can only work for 10 months instead of 12) because of this. You can apply for an OPT 90 days before you graduate (and 60 days after), but you can pick the date you want your OPT to start (up to 60 days after your graduation date). I was being stupid, and thought I could push the start date back if I applied later (after I graduated), but that only cut time off my already existing working time frame. OPT's take 3 months to process and get mailed to you. Meaning, I got the card (which employers require before you can start work) after my OPT period started. So basically I was not able to work when the time on my OPT was running. So, apply for it early!

Good resource: http://www.uscis.gov/eir/visa-guide/f-1-opt-optional-practical-training/understanding-f-1-opt-requirements