You can use Dual-band, Tri-band or Quad-band phones in the Netherlands provided that they can operate in the (European) GSM-UMTS networks. Don’t forget the high costs for both local calls and calls to outside of the Netherlands. A good alternative is to purchase a cheap prepaid phone in the Netherlands for the duration of your stay.
The bike tours are offered in the seasons when the local weather is pleasant (April thru to mid October). In April, early mornings can be chilly. Remember ... even in the summer you can sometimes be caught out by a shower of rain in Holland. After booking more clothing advices are available within your "My Bike Tour" account.
No, for the Netherlands no vaccinations are required.
Not as an EU, Canadian or USA citizen . Check whether you need a visa with the foreign affairs department or the Dutch embassy in your home country.