First thing you need to do is clarify the environmental situation. Lenders will not lend if there is an issue on any part of the property. That's because they can be dragged into liability for damage due to any contamination. Your state environmental agency can issue a no further action letter when the property's clean. That's the lender's green light to proceed. You may be eligible for a Brownfields agreement, but my experience is these arrangements take a long time for the remediation plan to be approved, and longer for the clean up. You might check with your local municipality to see if they have any block grant money for remediation. Also did you have an environmental indemnity in the lease with the trucking company? You might find a lender once you've been accepted to the program. It's essential to have a good environmental consultant to guide you.
I haven't been involved in cannabis yet, but I have talked to lenders who will fund these businesses. This is private money, not cheap. Also few banks will allow deposit accounts or merchant processing for cannabis. This means they are cash businesses, subject to all risks associated with a lot of money on site. Cannabis is a rapidly consolidating sector, so this start up will confront business risks as any other in a fast growing industry.
As far as who pays for the new building, it's a point of negotiation. I've seen it both ways. Since you are eligible for cannabis, it might be worth while to approach others in the industry with a development plan. You could get a better deal than the one on the table.
I work with an investment group that specializes in turning around troubled properties. You can PM me if you'd like to discuss further. Good luck!