I have done this in the past and it was pretty easy. I think a setting has changed that disabled the way I used to go about this. Here is the code for my current slideshow that is embedded into canvas:
<p><iframe src="https://docs.google.com/presentation/d/e/2PACX-1vSGIhVcwIt7J7vvy6ySyX3J7hrqLBYrCQaGTqPTQP1LFqHBYmlm93qE73iVdpaQ3eEqZoK9wS3BjMN5/embed?start=false&loop=false&delayms=3000" width="100%" height="569" allowfullscreen="allowfullscreen" webkitallowfullscreen="webkitallowfullscreen" mozallowfullscreen="mozallowfullscreen"></iframe></p>
I used to be able to simply put "#slide=3" in between the "delayms=3000" and "width" portion that is underlined and in pink up above if I wanted the slideshow to automatically open up with the third slide - as opposed to making users click through the presentation to find the most recent and relevant information.
Now every time that I do this, the inserted information just disappears and the function does not work. Is there a way to tell the embedded slideshow to automatically open up and stay on a specific slide?