Connecting MSA 2312i and P2000 G3 SAS MSA together

[Bpdzenith]

Hello were adding an additional storage controller P2000 G3 and DL380p G8 to our existing setup to host VM's using ESXi

Set up 

Existing (at capacity) 

1x DL380p G7

1x MSA2312i

New 

1x DL380p G8

1x P2000 

ideally we want to connect the 2 SANS together to act as one large unit rather than 2 SAN'S serving each ESXi Host individually am I right in thinking an external SAS cable would work in joining the 2 tegether to act as one large SAN

With both the storage controllers being in the storage works family are they compatible?

Many thanks