What you need to know before travelling to the USA and Canada from the UK:
ESTA (Electronic System for Travel Authorisation) for UK passengers. This is required for all forms of travel to the USA and costs approx $14 USD. The best place to obtain this is from the www.esta.cbp.gov search ESTA. ESTA lasts two years or earlier if your passport expires. You will need to re-apply for an ESTA if you have obtained a new passport. Most cruise lines request a passport with 6 months validity when travelling but check with the cruiseline.
When completing an ESTA online you will be asked if you are staying in the US or in Transit (passing through a US airport whilst tavelling to another country) If you are passing through tick "in Transit" if you are landing you can put the name of the hotel (you will need full address including postcode) or the cruiseline's office in the US.
ETA (Electronic Authorisation for UK). This is required for all UK passengers entering Canada by Air or transitting. You do not need this if visiting Canada by land or sea you just need a valid passport. The cost of this ETA is approx $7 CAD and again use the official site www.canada.ca search ETA. Canadian ETA lasts 5 years or earlier if your passport expires
BE AWARE: There are a lot of websites out there charging up to £100 for this service so be careful ...