Canadian wedding planner and event designer wanting to do business in the US
Technically you can do business in the US using your Canadian company (you would simply need to obtain an EIN for it and report its US income on a tax return).
It would of course help to have a US company that would be simply reselling the services of your Canadian company to US clients. For that matter you could register it in any state (I would suggest Wyoming or Delaware), and if you have the ability to travel to the US I would also suggest opening a US bank account for it.
As far as licensing goes, I haven't heard of any wedding planner licenses (I even checked Washington state license list, since they have a very long one, and haven't found any wedding or event planner licenses). But of course it would be necessary to check each and every state you plan to sell in, even though its highly unlikely that any state would have such a license.
You might need to get a reseller permit (sales tax ID), but only in those states where you have nexus and only if you sell to consumers in those states (and if your "product" is taxable in that state). Since you do all work and ship from Canada you would only have nexus in the state of formation, and if you don't have clients in that state you don't need to worry about sales tax.