A revised employer letter stating the new period and the duties for it, the current admission record, the documents that supported the original entry, and citizenship evidence. Whatever an extension route requires is added to that on counsel's advice.
Refresh the letter rather than annotating the old one
A support letter that still shows the original end date invites questions no one can answer cleanly. Ask the employer to issue a new letter covering the revised period, signed by someone who can speak to the duties. Keep the earlier version in the file so the sequence is visible, and make sure the two do not contradict each other on the professional role.
Save the dated posting and the employer’s explanation before updating the working documents. Keep the original contract, cancellation correspondence and any prior filing or entry record together. Preserve the genuine source record and provide the translation or explanation required for the applicable process. The teacher entry requires a baccalaureate in any field, so the bachelor of science alone suffices; bringing the bachelor of education as well does no harm. A Canadian may generally present the coherent package at a port of entry, while the employer may instead use Form I-129.