Not sure if you meant that your conference was cancelled OR visitor visa was cancelled. Anyways, hoping the conference was cancelled, YES, as long as your visa is valid, you can visit USA.
My parents have both US and Canadian Visitor's visa. We are planning to go to Canada (via road) for a 10 day trip. Any additional documents I need to carry with me (in addition to their passports) OR I need to take care of while entering US? TIA