fortigate 40c. Can i have 2 wan working in parallel???

Based on the following document the device has 2 WAN ports. I think it should allow you configure fail-over.

i do not want a failover configuration ,i want to summarize 2 wan speed....

If that's the case I recommend you have a look at the OS version that's running on the device right now, locate the corresponding manual for it on the SonicWall's website and review the available options to route the traffic.  
I'm not sure, but you also might be able to submit a ticket with SonicWall support to have them assist you and advise on the best configuration.

Load balancing sounds like something that would make far more sense for you. You would be able to spread out the load of connections over both WAN links, rather than having a failover configuration. https://docs.fortinet.com/uploaded/files/2144/fortigate-load-balance-528.pdf

Since you have 2 WAN ports connected to ISP's it's possible to configure your dual internet connection load balance,  But first, make sure your FG OS  Version Must be 5.2.1 or higher and It's called SD-WAN feature.

please note, before doing any config adjustment you have to take a backup of your FG configuration.
The link below shows you how to config dual internet connection.
https://cookbook.fortinet.com/redundant-internet-connections/