In Canada, you are applying for a new L1 Blanket using your company's already approved I-797 blanket approval notice. Even though you will get a new visa for 5 years, the PED (petition expiry date) ,will be your remaining time in the L1 Max out , ie 5 years. and the same PED will be your I-94 expiry date. Hope this answers your question.
But if you apply for I-94 extension through USCIS for your L1B individual, and if it is approved, and then you go for stamping, it will be still L1B individual..not Blanket