I'll try to offer some general advice.
First, I think YOU need to develop a solid go to market plan/strategy for the US market. I emphasize YOU in this because you won't be able to fully rely on rep firms to handle this for you. Some reps will be very experienced with this, while others (and I suspect most) will be able to provide only minimal help in getting you properly positioned in the US market.
You also want to develop your own strategy so that you have all firms operating under the same guidance. This will help eliminate confusion or crazy problems with situations that cross territories. Paying an experienced rep firm or consultant to help you draft a viable channel plan would probably be a good use of money.
Before you sign up too many rep firms, I think you will need a distribution and warehousing strategy in the US. You can try and pursue ADI/ScanSource/Anixter, or you can work with a 3PL company. If *I* were doing it, I'd probably explore the 3PL route rather than trying to become yet another unknown camera supplier to ADI/etc.
You're trying to break into a relatively crowded and competitive market. By entering now, you're going up against more established brands on both the high-end (Axis, Avigilon, Arecont, etc.) and the low-end (Dahua, Hikvision, etc.). You will need a very strong and very well articulated marketing position in order to get enough market share to make it worthwhile. I would not leave that solely to a rep firm, not because of any bias against rep firms specifically, but because I feel that is the sort of thing that YOU need to decide for your company (possibly with the *help* of a rep firm owner or consultant).
You'll also need to develop a good lead generation strategy. Some rep firms can help generate new leads, but a lot of them cross-pollinate things, meaning that if they represent Brand A, Brand B and Brand C, if they get a lead from Brand A they will try to also promote Brand B and Brand C in the meeting. But there is no guarantee the customer wants to see your "Brand B" camera, so their interest may be minimal. Or if the rep isn't getting a lot of interest in your product they may spend less time on it in meetings. However, if you're sending the reps leads and the customers are interested in your cameras and excited, that will give them more motivation to show it in more places.
Develop your distribution strategy if you haven't already. Get product in the US. Develop your marketing plan, and THEN you can go to rep firms with the intent of signing them up. That part will be easy, offer them an 8% commission to start and then promise of at least 4 leads per month and there should be some eager ones. Your other big obstacle might be finding a firm that doesn't already have 1 or 2 cameras lines, and in many cases those manufacturers will prevent them from taking on another competitive line.
With the Han-sung rebranding fiasco this could be a good time to target reps that were signed up with Samsung and offer them something more strategic.
If you're planning to be at ISC West I can take a few minutes to offer some additional guidance or possibly make a couple of intros to rep firms that might be a good fit.