Glad to hear that your client liked what they saw.
I've addressed your questions below.
Do you have a date when this App will be available as Alpha ?
The app has already passed the "Alpha" stage. This was when only the Method Solution Providers had access to the application. It is currently in the "Beta" stage but since it is a public beta now, anyone who has the invite code is able to install it. They just have to be cool with using a beta product and expect to have the odd bug.
Can a tax code be associated with an expense (for QB Canadian) ?
On the "Expense" screen, I wouldn't imagine that we would add an option for an employee or vendor to select a tax code. From my research, that isn't very common, at least at the level of an employee or vendor doing the data entry. If you wanted to customize Method to do that, or course that is always an option.
There is already an option to display a "taxes" field where you can enter the tax amount on a receipt. This can be turned on via Process Expenses > Preferences and checking the "Allow to enter taxes for expense?" checkbox. The next time that you open the Expenses screen, a field for "Total Taxes" will appear.
The one thing that I have on my to-do list is for the Expense Report to total the total amount of taxes at the bottom of the report.
Can a currency be associated with an expense (for QB Canadian) ?
This is a feature that we plan on adding in the future but isn't an option at the moment.
Hope that helps!