Your passports have to be valid for at least another 6 month after you return home. At the time of departure they should contain a minimum of 20 empty pages, more if you are the registered owner of the rig. Consulates are located in Tapachula and also in Comitan, both in the State of Chiapas. A tourist visa for US citizens is good for multiple entries and valid for 3 years. Canadians can obtain a tourist visa for 30 days only and have to apply for a new visa before entering Guatemala on the return trip.
Tourist visas are free of charge.
You require a Tourist Card, which you must obtain from a Consulate. There is one in Tapachula, Chiapas, any cabdriver will take you there. Another visa will be required on the return trip. At this border you will purchase a fiscal stamp, before your passport is stamped. This is also the obly border, where you will have to purchase insurance, to cover your medical attention, if required.