I just ran in to this error, and found a fairly simple fix.
Edit wp-stripe/includes/stripe-functions.php and find ‘usd’ and change that to ‘cad’ as follows:
function wp_stripe_charge($amount, $card, $name, $description) {
/*
* Currency - All amounts must be denominated in USD when creating charges with Stripe — the currency conversion happens automatically
*/
$currency = 'cad';
/*
* Card - Token from stripe.js is provided (not individual card elements)
*/
Then go to wp-stripe/includes/stripe-display.php and find ‘USD’ and change it to ‘CAD’ as follows (for display to the user):
<div class="stripe-row">
<input type="text" name="wp_stripe_amount" autocomplete="off" class="wp-stripe-card-amount" id="wp-stripe-card-amount" placeholder="<?php _e('Amount (CAD)', 'wp-stripe'); ?> *" required />
</div>
Cheers! Let me know if you need help.