Thanks for a quick answer

I did it

In mainnav.php change:

<div class="navbar-header">
to
<div class="navbar-header pull-right">

and

<button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".t3-navbar-collapse">
to
<button type="button" class="navbar-toggle pull-left" data-toggle="collapse" data-target=".t3-navbar-collapse">



in off-canvas.php change:

<button class="btn btn-primary off-canvas-toggle pull-right<?php $this->_c('off-canvas') ?>.....
to
<button class="btn btn-primary off-canvas-toggle<?php $this->_c('off-canvas') ?>.....



in style.less add:

// ---------------------------------------------------------
// MAINNAV
// ---------------------------------------------------------

@media screen and (max-width: @screen-xs-max) {
#t3-mainnav .navbar-header.pull-right {
float: none !important;
}
}

Hi Jacob,

There will be several changes to make the off-canvas-button float to the right.

1. Add "pull-right" to div "navbar-header" => <div class="navbar-header pull-right">...
2. You may need to add "pull-left" to the collapse button "navbar-toggle collapsed pull-left" if you want it float to the left.
3. You also need to add

@media screen and (min-width: @screen-sm-max) {

    #t3-mainnav .navbar-header.pull-right {

     float: none !important;

    }

  }

It require a bit CSS skill to do it.
You can hide a CSS Developer to help you if you have problem.

Regards