The difficulty for you is the fact that you are in the UK and your stepmother is in Canada and therefore, distance is not on your side.
Even if you had a court order to make her produce the will, if she genuinely doesn’t know where it is has destroyed it because it is not in her favour particularly, and there is no known copy anywhere, then the court cannot order an impossibility.
If he has not written a Canadian will and you cannot find one then his estate is dealt with under the rules of intestacy which are different in Canada than they are in the UK and it depends which province he is in you would need a Canadian lawyer to sort that out.
Regardless, his wife, under the rules of intestacy, will get a preferential share of his estate with a small balance coming to children. She would be treated as the next of kin as they were still married and it’s unlikely that a lawyer would get involved on your behalf unless she has said that she doesn’t want to administer the estate. The court will not usually get involved purely because someone is slow. You say that your father recently passed away. I don’t know how close they are but in cases like this, it is not unusual for grieving widows to wait several months before they can actually come to terms with dealing with their deceased husband’s estate.
With regard to her administration of the estate, if she simply refuses to do it, then you would be faced with making an application to court in Canada. The position with the house in the UK is that if he doesn’t have a UK will, it is dealt with under the UK rules of intestacy whereby she still gets the majority. The house in Italy would be dealt with under Italian law and those rules may be different than in the UK or Canada. Certainly, inheritance law in France is so different from UK law as to be unrecognisable.
Can I clarify anything for you?