Various shipping quotes - All based on same product, location & quantity

1) Your strategy of re-defining the maximum package weight should work fine, as long as you just change the define() statement at the beginning of uc_canadapost.module. It looks like the breaking into packages is working properly, because all your screenshots show 3 packages, which is what I would expect for 60 books.

2) The module doesn't use any settings in your SellOnline account package, so to be safe you shouldn't do things like add handling charges or ask SellOnline to box up items for you.

3) Dimensions of the box are not taken into account for the shipping quote. That should not matter, because books are heavy. The only situation where ignoring dimensions matters is when you have large boxes with light items in them - i.e. when the package is less dense than expected.

4) This module should *always* give the same rates as the Canada Post site, given the same inputs, because it is actually querying the Canada Post site and returning the results. If the rates are not the same, that implies that the module is not sending Canada Post the same information as you are manually entering on the Canada Post site. To debug this, go into the source code and remove the // in front of the two statements below:

    $xml = _uc_canadapost_make_request($package, $details);
    //drupal_set_message('<pre>'. check_plain(var_export($xml, TRUE)) .'</pre>');
    $response = _uc_canadapost_do_request($xml);
    //drupal_set_message('<pre>'. check_plain(var_export($response, TRUE)) .'</pre>');

Now, you will see the data sent to Canada Post, so you can tell exactly what weight this module is sending for each of your packages.

5) I don't know of any situation where this module could return different quotes for the same order. The module will always send the same data for a particular order, so Canada Post should always make the same response.

6) As to why the actual shipping charge differs from both the module quote and the Canada Post website quote, I suspect the actual conditions (weight of box, insurance/no insurance, etc.) may be different that what is being quoted. In principle the actual shipping charge should be the same as the quoted charge, unless there are factors affecting the price that aren't accounted for.

In summary, try uncommenting the debug statements to see exactly what is being sent to Canada Post. If Canada Post's response is wrong, there's not much I can do about it, but if the module is sending the wrong data, that might point to a bug.