No, patients cannot see their pending treatment plans in their patient portal. The only place where patients can view their pending treatment is in a communication from the treatment plan follow-up automatic communication (see Campaigns > Automatic Communications > Treatment plan follow-ups).
What a patient may be able to see in their portal is any past treatment performed, depending on your settings. You can edit what the patient sees in Settings > Patient Connect Portal.
If you show patients their past treatment, this is what it looks like to them: