Assuming that you ( a US citizen) are residing in Canada, to be able to file US tax return as MFJ ( Married Filing Jointly), you can either (a) download form W-7 from the IRS, fill it out, attach all the documents asked for and mail this in to the IRS OR (b) do nothing now, when you file your 2019 return, file as MFJ, print , sign ( both you and your spouse), fill out form W-7 , include all the attachments required, add a note -- signed by both of you -- stating that you both would like to have your spouse treated as a tax resident of the USA AND send the whole shebang to the IRS by mail. The former would result in issuance of ITIN perhaps before the filing date ( ?? ) while the latter will generally result in issuance of an ITIN for your spouse retrospectively i.e. for the year 2019 tax year.
I still suggest that you try and visit the IRS section as also the consular section of the nearest US consulate --- perhaps they can certify the documents ( passports , marriage cert etc. ) needed for an ITIN for your spouse. They will definitely have the latest on the subject.
Good Luck
