I am connecting a jacuzzi.. the manual says it is a 110v. However the motor is 220/240v. There is a built in GFI breaker that is labeled /accepts only a neutral and one live load wire and a third slot which not active (will not accept any wires) - is this possible?

Not sure.
Why not post a make and model of the tub so we can see the diagram or instructions for ourselves?

This is the website that lists all the data plus pic..
Luxurious Outdoor SPA (YD-11) - China Spa Bathtub, Luxurious Spa Whirlpool, Massage Spa Bathtub in Bathtub (http://spa-ymir.en.made-in-china.com/product/LeMxtyPbbQhN/China-Luxurious-Outdoor-SPA-YD-11-.html)
Appreciate the help

Oh great, Made in China.com. Well there is part of the problem.

The limited information given at the link you provided states the unit is rated 220 or 380 volts.

Sounds like you got the incorrect manual with the unit.

That site is a purchasing and distribution site. That is NOT the manufacturer.

They are only providing the list of specifications. The manufacturer is Ymir and I found this in about 30 seconds:
5-person spa,hot tub(YD-11)----GuangDong LianSheng Pool&Spa Equipments Co.,LTD.(Ymir Spas) (http://www.spa-ymir.com/en/displayproduct.html?proID=100355768)

Again, a basic list of specs. The voltage is show as: 220-240v/50-60hz, 380v/50hz, 110v/60hz
These are the available voltages, not the actual voltage for every unit.

This is a cheap Chinese import with I imagine almost no tech support in the US. You buy it and good luck to you.

With the information given I would have to bow out of this one. Sorry.

I would try and find a reputable electrician in your area to come out and read the specs and diagrams and make decisions based on that.