* do I need a visa
No the UK is part of the visa waver program so you should be fine with just your passport as long as it is still more then 6 months away from expiring. If you were flying you would need to get an Electronic System for Travel Authorization (ESTA), however I believe those are not required at land border crossings.
* Car wise .. any specific's insurance wise
You can double check with your insurance broker, but I believe most Canadian auto insurance polices will cover you in the US as well.
* Specific Accident insurance / health insurance
It is a good idea to get supplemental medical insurance when you are going to the USA as hospital fees there far outstrip what OHIP will pay for out of province care.
* anything to watch out for or be careful about
NY State assesses a driver responsibility fee for people who commit certain driving offences that gets added on top of what ever fine you get assessed. For example anyone caught going 21 mph over the limit or higher has to pay a $300 fee on top of their fine. NY state troopers are known to be pretty rigid in their application of the law so I would make sure not to speed or at least not excessively while there.