You can start with any lender you want, I always suggest a local one as they better know you, your market and processes.
You can start with your own bank, credit union or ask a great local agent if they have recommendations. Agents tend to know who gets the job done well with great pricing and minimal headaches.
You'll need a lot of personal information, 3 months bank statements, 2 years taxes and 30 days worth of pay stubs to get a meaningful pre-approval based on how the lender interprets your data versus how you might.
I hope this helps.