Let me address this by talking about the process required to engage employees from a broader perspective. In order to successfully engage them, you must educate them, inspire them and demonstrate relevancy, obtain a commitment to changed behavior, and reward and recognize them. I would suggest that you use this as a model to ensure that they embrace the system.
Specifically, make the effort to explain why you are making the change, what it means to the company, what it means to them personally and the tangible benefits. Training on actual use of the system is obviously important, but if you want them to embrace this, they need to share the vision and understand the strategy. You're not asking for their approval for the change, but people embrace change that they have an opportunity to participate in, rather than as a directive from leadership to adopt. I don't know if you did this or not, but during the process of deciding on the upgrade and moving to a single ERP system, it would have been a great idea to get input from employees who currently use it and share it in some type of social community to demonstrate buy-in for the change.
Next, make sure they understand how this benefits the company AND how it benefits them. Will it make their job easier? Will it allow the company to be more profitable? Will it drive new customer growth? They'll embrace change if it benefits the company but generally, when you ask someone to change, they want to know what's in it for them.... and it isn't necessarily a financial impact. Again, it may just be that it makes their job easier.
Finally, think about some kind of reward and recognition program for early adopters and for champions. It doesn't have to cost a lot. Intrinsic motivation goes a long way. People are inherently motivated by the desire to have some control, the desire to get better at something, being part of something larger than themselves, and connecting with others.