The 3-Day Canada East Coast Tour from New York runs Niagara Falls, Toronto, and the Thousand Islands in 3 days from $508.33. The 14-Day East Coast USA and Canada Tour from New York covers 2 Countries and 11 Cities in 14 days from $5,499.39. Same departure city, same border, eleven extra days, and the paperwork does not change.
Coming back by land or sea, the Western Hemisphere Travel Initiative sets the list: for an adult U.S. citizen, a passport, a passport card, an enhanced driver's license, a Trusted Traveler Program card such as NEXUS, SENTRI, or FAST, a military ID on official orders, or a Form I-872 card. The passport card is the trap, since it works for land and sea crossings and is not accepted for international air travel. Children under 16 traveling as U.S. or Canadian citizens need a birth certificate or other proof of citizenship. Arrive without a compliant document, and the likely outcome is a delay at the border.
Going into Canada, the requirement follows the mode of travel. By air, you need an electronic travel authorization and a valid passport to board. By land or sea, arriving by car, bus, train or boat, travelers from an eTA-required country usually do not need one and still need a valid passport, while nationals of visa-required countries need a visitor visa rather than an eTA on those crossings. U.S. citizens are exempt from the eTA. An eTA costs CAD $7; most approvals arrive within minutes, some take several days, and the advice is to apply before booking the flight.

Mexico runs a form instead of an authorization. Every foreign national traveling to Mexico for less than 180 days fills a Multiple Immigration Form, the FMM, which has a maximum validity of 180 calendar days and covers a single entry. Air arrivals use the FMMD, land arrivals the FMME, with the electronic land version available in Baja California, Sonora, Chihuahua, Coahuila, Nuevo Leon and Tamaulipas. You print it and carry it to the crossing point. The fee paid for the condition of stay is not a guarantee of entry: the form records an intention, and an officer decides.
That is why responsibility sits with the traveler even on a fully guided departure. A guide can walk a group to the counter and translate. The declaration, the eTA application, and the FMM belong to the person whose name is on the passport, and no departure absorbs a missing document.