The Whirlpool Bridge is the oldest of the Niagara crossings, built in the 1800s, and space for facilities is limited. US and Canada jointly limited the use of that particular bridge to NEXUS cardholders only. You can't even drive across it without a NEXUS card.
Assuming a taxi driver had a NEXUS card, which is probably somewhat likely as a frequent border crosser, they wouldn't be able to take you across that bridge unless you were also a NEXUS cardholder. It is forbidden to use NEXUS lanes unless all passengers are NEXUS, and they revoke NEXUS privileges if you try it. A taxi driver would not try it, NEXUS privileges are pretty useful and they wouldn't want to risk them. Both Canada and the US are pretty zealous about enforcing NEXUS rules and NEXUS members are expected to know and strictly abide by them.
It isn't like there aren't alternate routes.